The purpose of this project is to characterize the blood groups, allotypes, and biochemical polymorphisms of rhesus monkeys (Macaca mulatta) and to use these parameters as markers in imunogenetic and reproductive studies. The controlled breeding program at the University of Wisconsin Regional Primate Research Center makes this colony uniquely suited for such studies. Since one of the missions of the Center is to obtain basic information in reproduction, the immunogenetic parameters will be studied as to their relevance to this area. We have already demonstrated that maternal-fetal incompatibility for blood groups can result in transplacental alloimmunization and we are investigating why the newborn infant does not exhibit hemolytic disease despite the existence of conditions that cause it in humans. We have also discovered that some blood groups seem to show abnormal segregation which may reflect some sort of prezygotic selection. The relationship of these blood groups to those in humans will be investigated. We will search for blood group receptors, like the human Duffy antigen which seems to be the receptor for the malaria parasites, since the rhesus monkey is the natural host of certain malarial parasites. The 21 alleles in the 13 blood group systems and the biochemical polymorphisms (isozymes) which we have described provide a powerful tool for monitoring breeding records, solving disputed parentage cases, measuring inbreeding and calculating gene frequencies for population genetic studies.